As one method of mounting an integrated circuit (IC) package or a chip-shaped electronic component (mounting component) on a board by solder, there has been known of a method in which solder is melted by applying heat from a backside of the board (the surface opposite to the surface on which the electronic components are mounted). In this method, in order to melt the solder, it is required to heat the backside of the board to a much higher temperature than a melting temperature of the solder. As a result, bubbles are generated on the backside of the board of the solder joint section due to thermal stress. Furthermore, with this method, the electronic components are pressed by a machine when soldering. This would cause such a problem as short-circuit or misalignment in the soldered section.
In order to solve these problems, there is a method to mount electronic components on the board by self-alignment. Self-alignment is such an effect that the electronic component is lifted by surface tension and stress of the molten solder, and then self-aligns itself on the mounting position on the board by restitution from the stress. In other words, the self-alignment is such an effect of the surface tension of the molten solder that transfers an electrode of the electronic component toward an electrode of the board when the solder is melted by the application of heat and spread out on the electrode of the board.
Thus, the self-alignment can align the board and the electronic component being mounted on the board with high precision without forcibly causing the alignment. Therefore, self-alignment is drawing attention among mounting methods for mounting electronic components wherein alignment of high precision is required.
For example, in Non-Patent Document 1, it is disclosed that the alignment of the core of a fiber-optic cable and the center of a light-receiving element is performed by self-alignment. In Non-Patent Document 1, an optical member with the requirement of aligning in comparatively high precision is aligned by the self-alignment.
In addition, for example, in Patent Documents 1 and 2, it is disclosed that mounting of IC packages (Chip Scale Packages (CSP)) and chip-shaped electronic components is performed by self-alignment.
Specifically, in Patent Document 1, when mounting an electronic component such as so-called chip component (resistor, capacitor, or the like), or an IC component, on the printed board (surface mounting), positioning of the electronic component is performed by the self-alignment. In Patent Document 1, in order to smoothly perform the self-alignment, the printed board is ultrasonically oscillated at the time of mounting the electronic component.
On the other hand, in Patent Document 2, the effect of self-alignment is increased by appropriately arranging a shape (area) and position of a solder joint section (terminal land) of an IC package component (CSP).
Because the self-alignment utilizes the surface tension of molten solder as described above, the self-alignment has been applied in mounting comparatively light-weight components. For example, alignment such as IC packages (mounting of independent IC bare chips, QFP etc.) and chip-shaped electronic components has been performed by the self-alignment.
Patent Document 1
Japanese Unexamined Patent Publication, Tokukai, No. 2003-188515 (published on Jul. 4, 2003)
Patent Document 2
Japanese Unexamined Patent Publication, Tokukai, No. 2003-243757 (published on Aug. 29, 2003)
Non-Patent Document 1
Journal of Applied Mechanics, Vol. 62, JUNE 1995, 390-397.